Naser S. Al-Huniti

TRANSIENT THERMAL STRESSES IN A THIN ELASTIC PLATE DUE TO A RAPID DUAL-PHASE-LAG HEATING

Thermal stresses generated within a thin plate as a result of a fast heating rate are investigated numerically using the dual-phase-lag heat conduction model. The quantitative and qualitative predictions of the dual-phase-lag model for the thermal stresses are compared with the predictions of the diffusion (parabolic) and wave (hyperbolic) heat conduction models. It is found that the predictions of the three models differ in the early stages of the heating process and then give almost the same predictions as they approach the steady-state limit.Thermal stresses generated within a thin plate as a result of a fast heating rate are investigated numerically using the dual-phase-lag heat conduction model. The quantitative and qualitative predictions of the dual-phase-lag model for the thermal stresses are compared with the predictions of the diffusion (parabolic) and wave (hyperbolic) heat conduction models. It is found that the predictions of the three models differ in the early stages of the heating process and then give almost the same predictions as they approach the steady-state limit.

THERMOELASTIC BEHAVIOR OF A COMPOSITE SLAB UNDER A RAPID DUAL-PHASE-LAG HEATING

This work is concerned with the investigation of the thermoelastic response of a composite slab (a two-, thin-, metallic-layered plate) under the effect of an intense rapid heating applied to one side. The dual-phase-lag heat conduction model is used to derive the heat equation in each layer. The heat equations are solved using the Laplace transform technique and the Riemann-sum method. As a result, the thermal behavior, in the form of the temperature distribution along the thickness direction of the slab, is determined. The governing equation of plate deflection is formulated and solved for simply supported edge conditions. As a result, the plate deflections and the thermal stresses are calculated numerically using the finite difference method. Thermal stress distribution is found to depend on the temperature distribution in addition to the difference in the thermal and mechanical properties of the materials that compose the two layers.

BEHAVIOR OF THERMAL STRESSES IN A RAPIDLY HEATED THIN PLATE

Using the hyperbolic heat conduction model, thermal stresses generated within a rapidly heated thin metal plate are investigated numerically. The effects of different parameters such as the form, duration, amplitude, and penetration depth of the heating source on the temperature, thermal moment, deflection, and thermal stresses are studied. It is found that under ultra-fast heating of very thin plates, the hyperbolic heat conduction model must be adopted to model the thermal behavior.Using the hyperbolic heat conduction model, thermal stresses generated within a rapidly heated thin metal plate are investigated numerically. The effects of different parameters such as the form, duration, amplitude, and penetration depth of the heating source on the temperature, thermal moment, deflection, and thermal stresses are studied. It is found that under ultra-fast heating of very thin plates, the hyperbolic heat conduction model must be adopted to model the thermal behavior.

Computation of Member Stiffness in Bolted Connections Using the Finite Element Analysis

Abstract In the design and analysis of bolted connections, it is essential to determine the stiffness of each element in the connection: the bolt and the members. While the stiffness of the bolt is easily computed as a bar in simple tension, the members stiffness, however, is much more complex. In this work, finite element analysis is used to compute the member stiffness in bolted connections. Two- and three-dimensional models are constructed and analyzed. Analyses are performed for joints containing members made of steel, aluminum, copper, and cast iron. In each case, the material is assumed to be linearly elastic and isotropic. The effect of the joint geometry on the member stiffness is investigated by constructing models with different aspect ratios that contain the most reasonable design values. Comparison with existing previous works and analytical models is performed. Empirical functional relationship is determined for the dimensionless stiffness.

Dynamic simulation model for mixed-loop planar robots with flexible joint drives

A dynamic simulation model for mixed-loop planar robots with flexible joint drive and servo-motor control is developed. The motion of the links is coupled with the deflection of the drive shaft at the joints. The virtual work method is used for the derivation of the mathematical model. The drive signal at the motor is based on the error between the desired and actual motions using proper position and velocity gains. Different motion programs are considered in the simulation for the time histories of the angular displacements and velocities of the links and motors. The driving torques and the total error produced at the end-effector are computed. The simulation results for a five-link, three degrees of freedom manipulator show that the model presented is capable of simulating the coupling effect of joint flexibility and rigid body motion for planar robots.

TRANSIENT VARIATIONS OF THERMAL STRESSES AND THE RESULTING RESIDUAL STRESSES WITHIN A THIN PLATE DURING WELDING PROCESSES

Variations of thermal and residual stresses are investigated inside a thin mild steel plate during welding processes. The temperature distribution is determined analytically using Greens functions. Transient thermal stresses developed within the plate are computed numerically. The resulting residual stresses, which remain after cooling of the plate, are found based on a method presented originally by Tall (L. Tall, Welding Journal, vol. 43, pp. 10–23, 1964). It is found that welding speed and heat source intensity are the main factors that affect the residual stress formation in the plate.

THERMALLY INDUCED VIBRATION IN A THIN PLATE UNDER THE WAVE HEAT CONDUCTION MODEL

Thermally induced vibration in a thin plate under a thermal excitation is investigated. The excitation is in the form of a suddenly applied laser pulse (thermal shock). The resulting transient variations of temperature are predicted using the wave heat conduction model (hyperbolic model), which accounts for the phase lag between the heat flux and the temperature gradient. The resulting heat conduction equation is solved semianalytically using the Laplace transformation and the Riemann sum approximation to calculate the temperature distribution within the plate. The equation of motion of the plate is solved numerically using the finite difference technique to calculate the transient variations in deflections.

Dynamic Thermoelastic Response of a Heated Thin Composite Plate Using the Dual-Phase-Lag Heat Conduction Model

This paper investigates the dynamic thermoelastic response of a heated thin composite plate. The plate is composed of a dominant matrix domain and an insert domain. A step-function heat source is generated within the matrix domain, causing the heating of the whole plate. The dual-phase-lag heat conduction model is used to determine the thermal behavior of the plate in the form of the spatial and time variations of the temperatures in both domains. The temperature of the matrix is used to evaluate the thermoelastic behavior of the plate in the form of the induced displacements and thermal stresses. The Laplace transformation technique combined with the Rieman-sum method is used to calculate the temperatures. The finite difference method is used to solve the governing equation of plate deflection and then calculate the thermal stresses. The resulting thermal stresses are found to be compressive and follow the same behavior as that of the temperature.

THERMAL STRESSES IN A RAPIDLY HEATED PLATE USING THE PARABOLIC TWO-STEP HEAT CONDUCTION EQUATION

This work studies the thermal stresses generated within a rapidly heated thin metal plate when a parabolic two-step heat conduction equation is used. The effect of different design parameters on the thermal and stress behavior of the plate is investigated.This work studies the thermal stresses generated within a rapidly heated thin metal plate when a parabolic two-step heat conduction equation is used. The effect of different design parameters on the thermal and stress behavior of the plate is investigated.

Constitutive Modeling for the Simulation of the Superplastic Forming of AA5083

The AA5083 alloy is already being used in applications that require lightweight construction and moderate strengths. In order to carry out accurate simulations of the superplastic forming of this alloy, the used constitutive models should be able to predict the deformation and thinning behavior during the forming process. In this paper, we compare the dome height and pole thickness evolution during gas bulge forming using different AA5083 constitutive material models. The models considered have different levels of complexity and are fitted using either tensile or biaxial experimental data. The simulation results are also compared with experimental data from literature. In addition, recommendations are made for developing accurate material models for the considered AA5083 alloy.